Robot with joints of variable rigidity and method for calculating said optimized rigidity

1. A robot with capabilities of displacement on at least one jointed chain comprising: at least one sensor of contact of an end of an at least one jointed chain with a displacement surface, said at least one jointed chain including at least one joint, said at least one joint driven by an electric motor controlled by an order determined based on a position and/or a velocity and based on limiting a current and/or a torque applied to said electric motor, wherein said limiting is controlled as a function of the torque applied to said at least one joint, said torque being calculated as a solution of an equation modeling a dynamic equilibrium of the robot between: a first sum of: (i) a difference of inertial forces due to an angular acceleration of the at least one joint, (ii) the gravitational acceleration, (iii) an effect of Coriolis forces, and (iv) centrifugal forces, and a second sum of: (i) the torque, (ii) contact forces, (iii) friction forces, and (iv) perturbation forces, said torque and said contact, friction and perturbation forces being applied to said at least one joint, wherein a part of effects of the inertial forces due to the angular acceleration of the at least one joint, effects of the Coriolis forces and centrifugal forces, and effects of the friction forces being modeled by an offset to a variable rigidity coefficient, and wherein said friction forces are limited by the variable rigidity coefficient calculated for the at least one joint.

2. The robot of claim 1 , wherein said offset varies according to a posture of the robot.

3. The robot of claim 1 , wherein the effect of the gravitational acceleration is calculated based on a matrix of inertia coefficients dependent on the configuration of the robot and applied to articular angles and of gravity vector determined by combining measurements of an inertial platform of the robot.

4. The robot of claim 3 , wherein for a calculation of the gravity vector, a disambiguation is carried out by determining an orientation in space of a central chain of the robot by solving for a position of effectors affixed to said central chain.

5. The robot of claim 3 , wherein points of application of the contact forces taken into account in the dynamic equilibrium model of the robot are determined by generating a first list of the effectors satisfying a criterion chosen from a group of criteria comprising: a first list of on/off states of contact sensors positioned on said effectors, a second list of thresholds of minimum distance with respect to a virtual ground plane of said effectors and a combination of said first and second lists, said criteria being substantially determined by a morphology of the robot.

6. The robot of claim 5 , wherein the effectors of the first list of on/off states are filtered into a third list by comparing a current posture of the robot with standard postures stored in robot configuration data, said standard postures determining a standard list of effectors, said third list comprising only the effectors of the third list corresponding to the standard posture adopted as closest to the current posture of the robot according to a similarity criterion, when it exists.

7. The robot of claim 3 , wherein the contact forces at points of application are determined by searching for a substantially optimal solution to the equation modeling the dynamic equilibrium between a third sum of said contact forces and a weight of the robot, and of a vertical component of the perturbation forces.

8. The robot of claim 7 , wherein the perturbation forces are neglected for the substantially optimal solution.

9. The robot of claim 1 , wherein the variable rigidity coefficient of the at least one joint is calculated by dividing the torque calculated for the at least one joint by a maximum torque defined for the robot.

10. The robot of claim 9 , wherein the maximum torque defined for the robot is modified as a function of a temperature measured at a measurement point on the robot.

11. A method comprising: limiting a torque and/or a current applied to an electric motor for driving a joint of a robot with capabilities of displacement on at least one jointed chain including at least one sensor of contact of an end of said at least one jointed chain with a displacement surface, said at least one jointed chain comprising at least one joint, said electric motor being controlled by a command based on a position and/or a velocity, wherein said limiting takes place by determining a calculated torque value applied to said at least one joint, said torque being calculated as a solution of an equation modeling a dynamic equilibrium of the robot between: a first sum of: (i) a difference of inertial forces due to an angular acceleration of the at least one joint, (ii) the gravitational acceleration, (iii) an effect of Coriolis forces, and (iv) centrifugal forces, and a second sum of: (i) the torque, (ii) contact forces, (iii) friction forces, and (iv) perturbation forces, said torque and said contact, friction and perturbation forces being applied to said at least one joint, wherein a part of effects of the inertial forces due to the angular acceleration of the at least one joint, effects of the Coriolis forces and centrifugal forces, and effects of the friction forces being modeled by an offset to a variable rigidity coefficient, and wherein said friction forces are limited by the variable rigidity coefficient calculated for the at least one joint.

12. A non-transitory tangible computer readable medium comprising computer program including program code instructions thereupon configured to be executed on a computer, said code instructions being executed by a processor for: limiting a torque and/or a current applied to an electric motor for driving a joint of a robot with capabilities of displacement on at least one jointed chain including at least one sensor of contact of an end of said at least one jointed chain with a displacement surface, said at least one jointed chain comprising at least one joint, said electric motor being controlled by an order based on a position and/or a velocity, said code instructions comprising code instructions for limiting the torque and/or the current applied to said electric motor, wherein said limiting code instructions are configured to execute said limiting as a function of the torque applied to said at least one joint, said torque being calculated as a solution of an equation modeling a dynamic equilibrium of the robot between: a first sum of: (i) a difference of inertial forces due to an angular acceleration of the at least one joint, (ii) the gravitational acceleration, (iii) an effect of Coriolis forces, and (iv) centrifugal forces, and a second sum of: (i) the torque, contact forces, (iii) friction forces, and (iv) perturbation forces, said torque and said contact, friction and perturbation forces being applied to said at least one joint, wherein a part of effects of the inertial forces due to the angular acceleration of the at least one joint, effects of the Coriolis forces and centrifugal forces, and effects of the friction forces being modeled by an offset to a variable rigidity coefficient, and wherein said friction forces are limited by the variable rigidity coefficient calculated for the at least one joint.